1. Field of the Invention
The present invention relates to a zoom lens system, and particularly to a small-size and low-cost zoom lens system for forming a real image on a digital or non-digital image pickup device of a camera.
2. Description of Prior Art
In recent years, most electronic devices, such as mobile phones, personal digital assistants (PDAs) and notebook computers, have been integrated with a photographic lens module for effecting the photographic function. Such a photographic lens module is generally required to be small in size and light in weight for portability, while providing a high level of image resolution. To satisfy these requirements, a conventional photographic lens module generally consists of three lens groups.
With the development of semiconductor technology, aspheric lens elements have been widely used in a photographic lens module. Conventionally, a photographic zoom lens system generally employs three lens groups in a negative-positive-positive refractive power configuration, wherein two of the three lens groups are movable for realizing zooming. However, the movement ranges of the two movable lens groups are relatively large, and the imaging performance dramatically varies with the increase of zoom ratio. To overcome these disadvantages, a zoom lens system consisting of four lens groups has been introduced. However, the employment of four lens groups leads to increase in the number of constituent lens elements and thus increase in manufacturing costs. Therefore, how to provide a high-resolution image with a minimum number of the component lens elements so as to still satisfy the compactness requirement is a challenge to be addressed in the art.
Hence, an improved zoom lens system, which is compact in size and low in cost while ensuring a high level of image performance, is desired to overcome the above problems encountered in the prior art.